1. Field of the Invention
This invention relates to a capacitive peaking method for bandwidth enhancement of transimpedance amplifier, more particularly, to a bandwidth enhancement method that can provoke a transimpedance amplifier to create pole-peaking effect by taking advantage of an extra capacitor.
2. Description of the Prior Art
In a highly developed optical network communication system, message in bulky volume are transmitted from second to second, this can be done so far by using optical elements and a wide-band preamplifier, which is considered a key role in optical signal receivers. In research of advanced techniques or amplifiers for massive data communication, the transimpedance amplifier is one of the preamplifiers occasionally applied in the optic fiber signal transmission.
In the so-called peaking technique of inductive peaking (L-peaking) transimpedance amplifier, an inductor is applied to double the bandwidth when peaking effect occurs in high-frequency band. As shown in FIG. 1, an inductor is used in peaking technique of the present transimpedance amplifier for creating circuit oscillation to cause peaking effect at high-frequency band and broaden bandwidth accordingly. Unfortunately, the area occupied by the inductor is far larger than that by an amplifier to waste space, and the accompanied stray capacitance may degrade the gain of the amplifier.
An optoelectronic receiver consisting of a photodetector and a transimpedance amplifier is used to convert optical signals into electrical signals in the front end of the optical fiber communication, therefore, a high-speed transimpedance amplifier is deemed a key role in design of the optoelectronic integrated circuits. For promoting signal transmission efficiency, this invention is proposed to substitute a capacitor for the inductor to broaden bandwidth of a transimpedance amplifier. The substituted capacitor will not impose any burden to the fabrication process in any way while its insulation layer can protect the circuits on the other hand.
Moreover, the capacitive peaking (C-peaking) method of this invention for bandwidth enhancement of transimpedance amplifier is applicable basing on xcexcm gate-length technology without changing the existing fabrication process.
The primary object of this invention is to provide a bandwidth enhancement method that can broaden workable bandwidth by adding a peaking capacitor to a transimpedance amplifier for creating pole-peaking effect, wherein the participated capacitor can provide an extra pole to reduce circuitry phase margin to thereby cause the peaking effect.
Another object of this invention is to provide a bandwidth enhancement method that can broaden workable bandwidth by adding a peaking capacitor to a transimpedance amplifier for creating pole-peaking effect, wherein the capacitive peaking technique is capable of doubling the workable bandwidth of the transimpedance amplifier without sacrificing the low-frequency gain, and further, the small sized capacitor benefits control of chip area.
Yet another object of this invention is to provide a bandwidth enhancement method that can broaden workable bandwidth by adding a peaking capacitor to a transimpedance amplifier for creating pole-peaking effect, wherein a simple method for evaluating capacitance of the peaking capacitor may be applied for design of a widest bandwidth of the transimpedance amplifier instead of doing it by trial-and-error.
A furthermore object of this invention is to provide a bandwidth enhancement method that can broaden workable bandwidth by adding a peaking capacitor to a transimpedance amplifier for creating pole-peaking effect, wherein occupied area of the peaking capacitor is far smaller than that of a peaking inductor as mentioned, and besides, an insulation layer of a MIM capacitor can meanwhile serve for a circuitry protection layer and an anti-reflecting coating layer for a photodetector in optical fiber communication receivers.
The bandwidth enhancement method of this invention is applied to broaden workable bandwidth by adding a peaking capacitor to a transimpedance amplifier for creating pole-peaking effect without changing framework of the original circuit and DC gain of the amplifier.
For more detailed information regarding this invention together with further advantages or features thereof, at least an example of preferred embodiment will be elucidated below with reference to the annexed drawings.